The Weichselian glaciation is the glaciation of the northern parts of Europe in the Last Glacial Period. It corresponds to the Würm glaciation in the Alpine region. It was characterized by a large ice sheet (the Fennoscandian ice sheet) that spread out from the Scandinavian Mountains and extended as far as the east coast of Schleswig-Holstein, northern Poland and Northwest Russia. This glaciation is also known as the Weichselian ice age (German: Weichsel-Eiszeit), Vistulian glaciation, Weichsel or, less commonly, the Weichsel glaciation, Weichselian cold period (Weichsel-Kaltzeit), Weichselian glacial (Weichsel-Glazial), Weichselian Stage or, rarely, the Weichselian complex (Weichsel-Komplex). In Northern Europe it was the youngest of the glacials of the Pleistocene ice age. The preceding warm period in this region was the Eemian interglacial. The last cold period began about 115,000 years ago and ended 11,700 years ago. Its end corresponds with the end of the Pleistocene epoch and the start of the Holocene. The German geologist Konrad Keilhack (1858–1944) named it using the German name (Weichsel) of the Vistula (Polish: Wisła) in present-day Poland.
Naming in other parts of the world In other regions Major Glacial 4 of the Pleistocene is given a local name. In the Alpine region it is the Würm glaciation, in Great Britain the Devensian glaciation, in Ireland the Midlandian glaciation and in North America, the Wisconsin glaciation.
Development of the glaciation
Early and Middle Weichselian The Fennoscandian Ice Sheet of the Weichselian glaciation most likely grew out of a mountain glaciation of small ice fields and ice caps in the Scandinavian Mountains. The initial glaciation of the Scandinavian Mountains would have been enabled by moisture coming from the Atlantic Ocean and the mountains high altitude. Perhaps the best modern analogues to this early glaciation are the ice fields of Andean Patagonia. Since the proximity to the temperate North Atlantic typically precludes ice growth in Scandinavia, changes in the North Atlantic are thought to be required for glaciation to develop in Scandinavia. The freezing and glaciation of the Canadian Arctic Archipelago could effect this by causing "relatively fresher" water from the Arctic and the North Pacific to flow east of Greenland disrupting the convection of North Atlantic Deep Water. According to this view any closing of the Bering Strait that blockades the entering of North Pacific water to the Arctic Ocean would have been detrimental for the inception of the Scandinavian Ice Sheet. Jan Mangerud posits that parts of the Norwegian coast were likely free from glacier ice during most of the Weichselian prior to the Last Glacial Maximum. Between 38 and 28 ka BP there was a relatively warm period in Fennoscandia called the Ålesund interstadial. The interstadial receives its name from Ålesund Municipality in Norway where its existence was first established based on the local fossil record of shells.
Last Glacial Maximum
The growth of the ice sheet to its Last Glacial Maximum extent began after the Ålesund interstadial. By circa 26 ka BP, the Fennoscandian Ice Sheet reached the mid-Norwegian continental shelf break. The growth of the ice sheet was accompanied by an eastward migration of the ice divide from the Scandinavian Mountains eastwards into Sweden and the Baltic Sea. As the ice sheets in northern Europe grew prior to the Last Glacial Maximum, the Fennoscandian Ice Sheet coalesced with the ice sheet that was growing in the Barents Sea 24 ka BP (kiloannī or one thousand years Before Present) and with the ice sheet of the British Isles at about thousand years later. At this point the Fennoscandian Ice Sheet formed part of a larger Eurasian ice sheet complex—a contiguous glacial ice mass which spanned an area from Ireland to Novaya Zemlya. The central parts of the Weichsel ice sheet had cold-based conditions during the times of maximum extent. This means that in areas like north-east Sweden and northern Finland pre-existing landforms and deposits escaped glacier erosion and are particularly well preserved at present. Also during times of maximum extent the ice sheet terminated to the east in a gently uphill terrain meaning that rivers drained into the glacier front and large proglacial lakes built up. The Last Glacial Maximum extent was first reached 22 ka BP in the southern boundary of the ice sheet in Denmark, Germany and Western Poland (Sławskie Lake District and Leszczyńskie Lake District). In Eastern Poland, Lithuania, Belarus and Pskov Oblast in Russia the ice sheet reached its maximum extent about 19 ka BP. In the remainder of northwestern Russia the largest glacier advance occurred 17 ka BP.
Deglaciation up to Younger Dryas As the ice margin started to recede 22–17 ka BP Denmark (except Bornholm), Germany, Poland and Belarus were ice-free 16 ka BP. The ice margin then retreated until the Younger Dryas when the ice sheet stabilized. By this time, most of Götaland, Gotland, all of the Baltic states and the southeastern coast of Finland had been added to the ice-free regions. In Russia, Lake Ladoga, Lake Onega, the bulk of Kola Peninsula and the White Sea were free from ice during the Younger Dryas. Before the Younger Dryas, deglaciation had not been uniform and small ice sheet re-advances had occurred forming a series of end-moraine systems, notably those in Götaland. During deglaciation, meltwater formed numerous eskers and sandurs. In north-central Småland and southern Östergötland part of the meltwater was routed through a series of canyons. It is speculated that during the Younger Dryas a small glacier readvance in Sweden created a natural lock system that brought freshwater taxa such as Mysis and Salvelinus to lakes like Sommen that were never connected to the Baltic Ice Lake. The survival of these cold-water taxa into the present-day means they are glacial relicts.
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